Most current designs of total joint replacements make use of bone cement to fix the artificial joint component to the bone. Prostheses which are primarily fixed to the porous inner part of the bone, called cancellous bone, sometimes fail after several years of use, causing much suffering to patients and a high financial cost for additional surgery to remove the failed prosthesis. Loosening of the prosthesis has been indicated as a primary cause of mechanical failure. Stress analysis of prosthesis designs is carried out numerically using the finite element method. To make use of this method, accurate three-dimensional stiffness data are needed for all components of the prosthesis-cement-bone structure. It has been suggested that deeper penetration of the cement into the pores of cancellous bone will enhance the success rate of the prosthesis. This idea creates a layer of a cement-bone composite, the properties of which are not known. In the proposed study the elastic constants of the cement-bone composites will be determined by a pulse transmission ultrasonic technique. Specimens of bovine and human cancellous bone will be cut in the form of 5 mm cubes from larger segments of cancellous bone, after filling the pores of the bone with bone cement. The composite material thus obtained will be assumed to be orthotropic and all nine elastic constants will be determined. This information is expected to be of direct use in finite-element analyses of orthopaedic implants.